Synthetic oil additive



2,999,067 SYNTHETIC OIL ADDITIVE Thomas F. Banigan, Jr., Walnut Creek,Calif., assignor to 'Iidewater Oil Company, San Francisco, Calif., acorporation of Delaware 1 No Drawing. Filed Nov. '27, 1956, Ser. No.624,493 9 Claims. (Cl. 252F-49.8)

This invention relates to a new family of chemical compounds comprisinga group of linear polymeric esters, particularly useful asviscosity-index improvers for certain types of synthetic lubricatingoils. The invention also relates to synthetic lubricating oil chosenfrom the group consisting of the diesters and the phosphate estershaving an improved viscosity index as a result of addition of compoundsof this invention. The invention further relates to a method forproducing the new family of compounds and to a method for improving theviscosity indices of certain synthetic ester lubricating oils.

In recent years synthetic lubricants have been developed in an attemptto meet the stringent requirements of new engines, including jetaircraft engines. These are superior to hydrocarbon oils in theirability to withstand temperatures as high as 450 without breaking down.They also flow at 65 F. and possess numerous other qualities enablingthem to perform well under diflicult conditions.

One class of such synthetic lubricating oil is usually referred to asdiesters. Examples are the (2-ethylhexyl) diesters, such as dioctylazelate, dioctyl sebacate, dioctyl glutarate, and dioctyl adipate. Inaddition there are various sebacates such as di-(methylethyl) sebacate,di-(3-rnethylbutyl) sebacate, di-(Z-ethylbutyl) sebacate,di-(l,3-dimethyl butyl) sebacate, di(undecyl) sebaeate, di- (tetradecyl)sebacate, and di(heptadecyl) sebaoate. There are corresponding adipates,azelates, and glutarates. There are other diesters such as1,6-hexamet-hylene glycol di-(Z-ethylhexanoate), tri-ethylene glycoldi-(Z-ethylhexanoate), and di-[2-(2'-butoxyethoxy)ethyl] adipate. Thereare also useful phthalate diesters, such as dibutyl phthalate(di-n-butyl orthophthalate). All these compounds may be grouped asdiester synthetic lubricating oils, or aliphatic branched-chain diestersthat remain liquid in the temperature range from about -30 F. to 300 F.

Another type of synthetic oil to which this invention relates comprisesthe phosphate esters such as tributyl' phosphate and tricresylphosphate.

The diester synthetic lubricating oils as a class possess high viscosityindices. However, some of the lowermolecular-weight members such asdioctyl adipate tend to be relatively deficient in this property, thuseliminating them from consideration as jet engine lubricants. It is thelower-molecular-weight diesters which offer the greatest promise for thefuture development of lubricants which will remain fluid at extremelylow temperatures. The phosphate esters have outstanding lubricitycharacteristics, excelling most other classes of synthetic oils. Lowviscosity index is probably the chief obstacle to their wider use asspecialty lubricants. It has therefore been a problem to produce anadditive which would increase the viscosity index in these two groups ofsynthetic oils, without causing trouble elsewhere. To do so is one ofthe objects of this invention, which accomplishes it by means of a newfamily of chemical compounds.

Another object of the invention is to provide a viscosity index improversuch that the improvement takes place when only a small quantity of theimprover is added, thereby not interfering with the other qualities ofthe synthetic lubricant and holding costs down.

2,999,067 Patented Sept. 5, 1961 ice The new compound broadly The newcompounds of the present invention comprise a new class of linearpolymeric esters, the class being delined by the general formula:

in which G represents a polypropylene glycol group of at least 7alkylene radicals joined linearly by ether oxygen atoms;

A represents an organic dibasic acid radical;

n is a number lying between 0.875 and 1.111;

x is an integer corresponding to the average degreeorf polymerization;and

R and R each represent an end group either or both of which may the ahydroxy radical, a carboxy radical, or an alkyl or aryl group.

The chemical nature of the end groups R and R with respect to thefunctioning of these polymers as viscosity index improvers, appearssecondary in importance to several other factors, including: (a) themolecular weight of the polypropylene glycol, (b) the dibasic acid used,and (c) the degree of polymerization. However, there have beenindications that the introduction of relatively nonpolar end groupshelps to protect the polymer from haze and color formation duringpreparation and is therefore preferable to the hydroxy and carboxy endgroups.

The polypropylene glycol group (G) Polymers prepared frompolyoxyalkylene .glycols composed of alkylene radicals of less than 3carbon atoms, such as polyethylene glycols, usually proved to he watersoluble and were invariably insoluble in the synthetic lubricating oilsdisclosed herein.

However, polymers prepared from polypropylene glycols have displayed therequisite solubility in the synthetic lubricating oils when saidpolypropylene glycols contained 7 or more oxypropylene units. Optimumactivity as a viscosity-index improver was noted with a polymer preparedfrom polypropylene glycol possessing 35 oxypropylene units. Onlyslightly less effective was the polymer made from a glycol with 17oxypropyleue Still soluble in synthetic lubricants, but much lesseffective, was the polymer made using a glycol with 8 oxypropyleneunits. The use of tripropylene glycol (3 oxypropylene units) gave riseto an insoluble polymer. The tests indicate that there should be atleast 7 oxypropylene groups, and there may he as many as 35 or 40.

T he dibasic acid radical (A) Various dibasic organic acids may be used.Excellent results are obtained where A is the oxalyl radical, butcarbonyl, succinyl, adipyl, sebacyl, isophthalyl, orthophthalyl, andterephthalyl radicals have also given good compounds.

Polymers prepared by reaction of polypropylene glycols (containing 7 ormore oxypropylene units) with dibasic acid chlorides (see thedescription of the method) ranging from oxalic to sebacic have all beenshown to be soluble in the synthetic oils claimed herein. However, thepolymers prepared using oxayl chloride have invariably been the mostpotent viscosity index improvers as well as possessing the least colorand haze. The somewhat greater reactivity of oxalyl chloride cornparedto the higher acid chlorides enables the use of lower reactiontemperatures, a condition which favors the production of a very highpolymer possessing a of color and haze.

The ratio of glycol to dibasic acid (G/A or n) Optimum results areusually obtained where equimolar ratios of glycol and acid halide areused. This favors a high degree of polymerization yielding a polymerwith 4 However, the use of non-polar end groups, those in (4) above,does give more clarity and freedom from haze and color formation.Typical compounds are shown in Table I below.

TABLE I Chemical composition of synthetic polyoxypropylene estersPolymer R R: A G I Viscos- G/A ities b #1 hydroxy hydroxy terephthalylnPPG1025 300 1.111 #2 do -do orthophthalyl. PPG1025. 475 1,111 #3polypropylene glypolypropylene gly- ..do PPG1025 1,500 0.875

col ether 65 4 col ether 65 d #4 hydroxy carboxyoxalyl PPG 1,200 1.000#5.- I1butyl.. n-butyl d PPG2025 00,000 0.875 #6.- ..do do do TPG 5,0000.950 #7. do do r1n PPG1025-.-. 20.000 0.875 #8 hydroxv carboxy adipylPPG2025 4,200 1.000

I PPG=polypropylene glycol, TPG=tripropylene glycol, and the numbersrefer to the average molecular weight, from which number of oxylakylencunits can be calculated.

b Viscosities at 210 F. in seconds Saybolt Universal are a function ofchain length.

* G/A refers to the ratio of glycol to dibasic acid.

Sold commercially by Carbide and Carbon Chemical Company under thetrade-name oi Ucon LB-tlfi, the 65 referring to the Saybolt Universalviscosity at 100 F.

great capacity for improving the viscosity index of certain syntheticoils. Polymers useful for this purpose can be obtained where the glycolto acid halide ratio lies within the range 0.875 to 1.111 and with endgroups R and R from any of the four choices enumerated below.

The degree of polymerization (x) It is difiicult to determine xprecisely because of the rather high molecular weight of the polymers;moreover, 1: appears to be capable of variation over wide limitsdepending on the molecular weight of the oxyalkylene glycol used in thepolymerization. A smaller x can give a useful polymer when a highmolecular weight glycol is used such as polypropylene glycol 2025 (apropylene glycol polymer having an average molecular weight of 2025)whereas a larger x is needed for a lower molecular weight glycol.Viscosity has been found useful as a guide to the required molecularweight. For example, polymers ranging in viscosity (210 F.) from about250 to 13,000 ccntistokes, and especially those from about 4000 to13,000 centistokes, have shown activity as viscosity index improves.Polymers of this same type with even higher viscositics should alsoprove useful if they posses the requisite solubility and shear stabilitycharacteristics (extremely high molecular weight polymers are oftendeficient in such properties).

The end groups R and R R and R will generally be:

1) An hydroxy radical in both cases if excess polyoxyalkylene glycol wasused in preparation,

(2) A carboxy radical in both cases if excess dibasic acid was used,

(3) One hydroxy and one carboxy radical, respectively, if equimolarreagent ratios were used, or

(4) An alkyl or aryl group, if excess dibasic acid dihalide is used toproduce a polymer possessing terminal acyl halide atoms capable offurther condensation reaction as with an alcohol or phenol, such asmethanol, ethanol, n-butanol, ethylene glycol monoethyl ether,diethylene glycol mono-n-butyl ether, polypropylene glycol monomethylether, tripropylene glycol mono-n-butyl ether, polypropylene glycol 425mono-n-butyl ether, phenol, paracrcsol, and nonylphenol.

As stated earlier, the end groups R and R are rela tively unimportant,merely a necessary chemical fact.

Some important qualities of each of these compounds are shown in TableII, the number assigned each polymer remaining the same through alltables and examples in this specification.

TABLE II Analytical data of synthetic polymers Polymer Acid Noe Sap. No.Vis. 210 Color 1 Acid N0.as in ASTM-D974-55T.

e Viscosities at 210 in Saybolt; Seconds Universal. 6Col0r-ASTl\iD-l5545T.

Methods of preparing the polypropylene esters Two preferred methods ofpreparation may be used: (1) ester exchange and (2) reaction of glycolswith dibasic acid dichlorides. The second method is an excellent one forresearch work, with high yields of high molecular weight polymers withminimum effort, while the first method uses cheaper and less reactiveintermediates and is therefore better suited to commercial manufacture.Examples of each type follow.

The two preferred methods are aspects or embodiments of a single broadconcept, namely, that of reacting polypropylene glycol with a dibasicacid derivative. The dcrivative is preferably chosen from the groupconsisting of the dibasic acid diesters and the dibasic aciddichlorides.

FIRST METHOD: ESTER EXCHANGE When the dibasic acid diester is used inthe method of preparing these polypropylene glycol esters, the reactiontakes place in the presence of a basic catalyst, such as sodiummethylate. Preferably, the reaction is conducted in an inert atmosphere,heat being applied so that the temperatures lie in the range between C.and 200 C. Methyl alcohol is formed as a by-product but may easily beremoved. Preferably, the reagents are diluted with some suitablesolvent, such as xylene, to prevent sublimation of the dibasic aciddiester. The following example of the first method (ester exchange)follows.

Example l.--Preparation of poly [polypropylene glycol 1025(])-terephthalate (9)] (polymer #1) by ester exchange The reaction wasconducted in a 1-liter, 3-necked, round-bottomed flask equipped with astirrer, a thermometer and a condenser with water trap, and providedwith a nitrogen atmosphere. The reagents proved to be miscible at about100 C. but further heat caused the terephthalate to sublime. Therefore,the contents were cooled, diluted with 100 ml. of xylene, mixed with 5g. of sodium methylate, and heated slowly to 170175 C. After three hoursof refluxing 19.5 ml. of methanol was removed azeotropically. Vacuum wasthen applied and the temperature raised gradually to 200 C. to removethe solvent and force the reaction toward completion. The prodnot wasobtained as 317 g. (97% theor.) of a straw colored resin. The crudepolymer was purified by dilution with three parts of pentane, followedby charcoal and clay treatment and filtration. On evaporation of thepentane from the filtrate the polymer was obtained as 291 g. of verypale viscous oil.

The polymer exhibited the properties tabulated in Tables I and 11 underpolymer #1. Also it had a refractive index 11 of 1.4664 and a specificgravity (sp. gr of 1.04.

SECOND METHOD: REACTION OF GLYCOLS WITH DIBASIC ACID DICHLORIDE Broadlyspeaking, the second method, that of reaction of glycols with dibasicacid dichlorides, is carried on in the presence of an acid acceptor,such as. pyridine or tributyl amine. Since the dichloride radical is theone to be removed, a still more accurate designation of the acidacceptor would be to say that it is an HCl acceptor. This reaction alsoforms a by-product, the-hydrochloride of the HCl acceptor, such aspyridine hydrochloride.

This reaction does not require a high temperature, and in fact may takeplace at low temperatures, around 5 to C. To insure completion of thereaction, the temperature may be gradually increased up to about as highat 85 or 90 C.less than 100 C. It has. been found preferable, though notessential, when using this method, to remove all the water by means of atrap prior to the halide addition, because such removal gives rise to ahigher degree of polymerization. The following examples illustrate thissecond method.

Example 2.Preparation of poly[polypropylene glycol 1025(7)-orth0phthalate (8).-p0lypr0pylene glycol ether 65 (2)] (polymer #3)by reaction of glycol with dibasic acid dichloride Another way ofstating the formula of this composition is O O H CH- O laaaaollt- JonahH I! where m is about 3 and n is about 17'.

0 \il H'll b The orthophthalyl' chloride diluited with an equal volumeof benzene was added dropwise to a stirred solution of the glycol and 47g. of pyridine dissolved in ml. of dry benzene. The temperature was heldat 10 C. by external cooling. Reaction was indicated by copious saltformation (pyridine hydrochloride). The polypropylene glycol ether(Carbon and Carbide Chemical Company Ucon LB .65) was mixed with 18 g.of pyridine and 50 ml. of benzene and was introduced dropwise after thechloride was in. The reaction mixture was diluted with additionalbenzene and stirred for about three hours at temperatures of 2545 C. Thepolymer solution was then filtered from the by-product pyridinehydrochloride, decolorized with charcoal and super eel, refiltered, andsolvent-evaporated to give 352 g. of yellow viscous resin.

In addition to the properties given in Tables I and II, the followingproperties were found for polymer #3: Refractive index 11 of 1.4689,viscosity at F. of 6875 Saybolt Universal Seconds, and a viscosity indexof 124.

Example 3.Prepararion of Poly[polypropylene glycol 2025 (1)-oxalate(1)](polymer #4) by reaction of glycol with dibasic acid dichloride Theglycol, molecular weight of 2025, and pyridine were mixed together withml. of dry benzene, placed in a reaction flask and cooled to 5 C. Theox-alyl chloride in an equal volume of benzene was then added dropwi'seduring one hour to the stirred reaction mixture held at 5-10 C. Anadditional 50 ml. of benzene was added, and stirring continued as thetemperature was gradually raised to about 85 C. The reaction mixture wasrefluxed for three hours and allowed to stand overnight. The product wasthinned with additional benzene and filtered to remove pyridinehydrochloride. The solvents were removed under vacuum with the aid of anitrogen bubbler to yield 290 g. (94% theor.) of virtually colorlessviscous resin. I

In addition to the properties noted in Tables I and II, the refractiveindex n was 1.4522.

Example 4'.-Preparation of poly [polypropylene glycol 2025(7)-oxalate(8)-n-butyl(2)]'(polymer #5) by reaction of the glycol withthe dibasic acid dichloride and with n-butyl end groups added 9 Anotherway of expressing the formula of this composition is wherein n averagesabout 34.

The glycol, pyridine and 200 ml. of benzene were refluxed until a totalof 0.5 ml. of water had been removed by means of a trap. (Thisexhaustive removel of water gave rise to a higher degree ofpolymerization than in Example 3.) The oxalyl chloride in benzene wasadded dropwise to the cooled, stirred solution as before. Extremeviscosity of the reaction mixture necessitated several dilutions withbenzene during the reaction period. The temperature was graduallyelevated to 85 C. and then cooled to 40 C. At this point a mixture ofn-butyl alcohol and pyridine was added dropwise. Stirring was continuedand the contents allowed to stand overnight. The mixture was dilutedwith 750 ml. of n-heptane and filtered. The filtrate was charcoaltreated, filtered and solvent-evaporated to yield 301 g. (95% theor.) ofextremely viscous pale yellow resin.

Example 5.-Preparati0n of poly[tripr0pylene glycol (I9)-oxalate(20)-nbutyl (2)] (polymer #6) by the method of Example #4 This reaction wasconducted according to the directions outlined for the preparation ofpolymer #5. All traces of water were removed by azeotropic distillationas before. The polymer was obtained as 99 g. (97% yield) of a veryviscous light amber resin.

Example 6.--Preparation of poly[polypropylene glycol 1025(7)-0xalate(8)-n-butyl (2)] (polymer #7) by the method of Example #4 3The reaction was conducted essentially according to directions outlinedfor the preparation of polymer #5.

Pyridine hydrochloride (by-product) formed copiously at the initialreaction temperature of 10 C. As the solution viscosity remained lowcompared to earlier preparations of oxalate polyesters, external heatwas applied to force the reaction. A reaction temperature of 85 C. washeld for about 3.5 hours following addition of the adipyl chloride tothe stirred glycol-benzene-pyridine solution. No noticeable increase insolution viscosity occurred after about three hours of refluxing. Theproduct resin was isolated as before to yield 309 g. (98% theor.) ofviscous straw'colored polymer. This resin showed a greater tendencytoward mineral oil solubility than did corresponding oxalates. However,it is still deficient in this property.

Use of the polymers of this invention as viscosity index improversRepresentative polymers of this invention were evaluated as viscosityindex improvers in various mineral oil stocks and in four of theprincipal classes of synthetic lubricating oils including (a) diesters,(b) polyglycol ethers, (c) silicones, and (d) phosphorous compounds. Thefirst thing tested was their solubility in the various oils, shown inTable III.

As Table III shows, these polymers had only limited solubility in themineral oil stocks including both solvent pale and bright stocks, sothey could not be used therein. They appeared to be completely insolubleand hence without efiect on the silicone oils tested. The polymers wereentirely miscible with the polyglycol ethers but later research showedthat they had no effect on the viscositytemperature characteristics ofthis class of synthetic oils.

The new polymers were very soluble in the diester oils and exhibitedhigh viscosity index activity, comparable and often better than thatobserved with the best available commercial VI improvers.

The excellent performances of some of these polymeric esters asviscosity index improvers for diester synthetic Reagents Wt" M0195 oilsare shown in the following Table IV.

grams Polypropylene glycol 1025 150 0. 146 Oxalyl chloride 21.2 0.167TABLE m n-Butyl alcohol 1 0.162 Pyridine 36.5 0. 461 Qualitativesolubzhties of synthetzc polymers Mineral Oil S thetl Oils This reactionwas earned out according to directions Stocks W e I for polymer #5 withspecial care again directed to trace P0X ymer water removal. The polymerwas obtained as 158 g. 150 Phos- Polyale right Diesters Silicones phatoglycol (99.5 ,0 theor.) of very viscous light brown resin. took EstersEsters Example 7.Preparation. of p0ly[polypr0pylene glycol PS 3 I s s2025 (1)-adipate(1)] (polymer #8) by the method of f g S 5 Example #4 PS3 I s 5 r S I s s I PS I I PB Reagents Wt., Moles I S I S S grams PS 8 IS S Polypropylene glycol 2025 300 0.148 Examples of synthetic oils usedfor these solubility determinations or 9 27.1 0.148 include:bis(2-ethylhexyl)sebacate, Dow-Corning silicone fluid 200, 25 0.320%cresIylBp3l6gsphate, and Carbon and Carbide Chemical Company b Scompletely soluble, PS =partia1iy soluble, I =insolub1e.

9. TABLE IV Viscosity index (A'STM D567) of polymer blends in diestersynthetic oils 10 TABLE V Viscosities and viscosity indices of polymerblends in tricresyl phosphate synthetic oil V Blend Vis. Vis. V.I. BlendV1s. VlsJ V.I. F. 210 F. 100 F. 210 k Dloctyl azelate 1 64.0 36.3 3 T il h t 1 Pl s 1% Polyme #3--- 67- 2 36. 9 142 r i iii; fi gi rer #5-.-.iii 33.; 33 Plus 2% Polymer #3.- 70. 7 37. 6 153 Plus 1.5% Polymer 18543. 4 50 Plus 1% Polymer e7. 5 37.0 145 10 Plus 2.0% Polymer #5. 202 41.s 66 Plus 2% Polymer #4. 71. 4 38.0 165 Plus 8.0% Polymer 235 47. 5 83Ens a? llzolymcr $5- fins 4.0% golymer #5. 275 50. 9 97 us 0 er a. 5.0 1Plus 3% Polfier #5 96. s 42. 5 17s us met #5 312 53 9 103 Plus 1%Polymer #7- 71. 1 37. 7 I 155 Plus 2% Polymer '79. 1 39. 4 182 lViscosities are seconds Saybolt Universal. Plus 1% Polymer #8..- 69.137.4 154 Plus 2% Polymer #8"; 74. 9 38.9 182 Dioctyl sebacate 1 68. 437.3 152 $2: Whether diester oils or phosphate ester oils are used, Plus1% Polymer 79. 9 39.1 168 it 1s not to be understood that the onlymaterials involved g3? Q2: 8%:3 it; are necessarily the oil and my newpolyester as a vis- D bPluls 2 galygmler #7 ggg 12g cosity indexunprover. As a mater of fact, other matei 11W P a a e rials not only maybe present but may be very desirable Pl 2 P01 er #5 72.9 37.0 111 I us mto prevent oxidation, 1nh1b1t rust, and for other reasons. 1 The dioctylazelate and diootyl sebacate were the bistZ-ethyl-hexyl) F01: exampleslilch antioxidants as phenyl alphanphthyl' esttlelrs fifhllillerespective acids; the dibutyl phthalate was di-n-butyl ammo, O12,6-d1tert-buty1 para cresol, O1 polymerized m- W t a 5 methyldihydroquinoline (sold under the trade-name Age- 2S dS bltU vesal.

econ S 0 m r R1te Resin D) are suitable antioxldants, and other wellknown antioxidants may also be used. Similarly, any of the well knownrust inhibitors or metal deactivators may be used too. Blending of theviscosity index improver with diester and phosphate ester syntheticlubricants may be accom- A most surprising and unexpected findingWas'the b6- plished by simple mixingi It may be desirable in some haviorf these polymers i i h h t t syninstances to prepare a concentratebecause the polyester thetic oils, where they were not only soluble butdisplayed vlscous F therefore be mwnvement to handle th d v in someapplicatlons. Thus, a small amount of tricresyl remarkable gfiectwenessmlsmg f phosphate synthetic oil or some suitable diester synthetic yPhosphate aster 0115 have excellent lubrlclty and oil may be used as thesolvent to carry the viscosity index noninflammability but arenotoriously poor in viscosityimprover into more of the same lubricant.This contemperature characteristics, a shortcoming which has 40 t l g ii? *E PF i t 1 O mos o o e v1scos1y-1n ex-nnproving p0 yes er.harflpered' the: moreover are general y me The concentrate also maycontam any of the ant1ox1dants Pailble Wlth and hence unresponslve tothe commercial mentioned above, or others. It may also contain rust in-ViSCOSiEY indeX impfovefs $11011 as the P y y P 3 hibitors, metaldeactivators, and other materials not inisobutylenes and polyvinyl otheThe compatability compatible with the lubncant or the polyester. andsusceptibility to viscosity index improvement which gicgi 3 522 3 9 anddesmbed the Pnnclples of has now been shown to result from the add1t1onof these 1. A lubricant composition consisting essentially of a newpolyoxypropyl glycol polyesters to P P' lubricant selected from thegroup consisting of diester ester oils serves to broaden the field ofusefulness of this lubricating oils and phosphate ester lubricatingoils, and class of synthetic oils. a sufiicient amount to increaseappreciably the viscosity o nds :to act as index of said lubricant of apolymerized polypropylene f m ablhty i these comp V glycol ester of anunsubstltuted, low molecular weight Vlscoslty Index P 13 shown by Tadibasic organic acid having a glycol-to-acid mol ratio in the range ofabout 0.875 to 1.111 and having a viscosity of at least 250 centistokesat 210 F. and with at least H (EH; (6

seven oxypropylene units in the polypropylene glycol radical.

2. The composition of claim 1 wherein the ester is wherein n averagesabout 34.

3. The composition of claim 1 wherein the ester is llafliiiliiaoilliiilwt.

where m is about 3 and n is about 17.

2,999,067 11 12 4. The composition of claim 1 wherein the polymerizedhas been exhaustively removed, and then reacting the ester has aviscosity between 250 and 13,000 centistokes glycol with a dibasic aciddichloride in a 1 1 at 210 F. th

5. The composition of claim 4 wherein the polymerized mol rang m therange between 0375 and L111 6 presence of an HCI acceptor at atemperature 111 the ester is present in an amount between 1% and of the5 lubricant range between 0 C. and 100 C. sald'polymer having a 6.Dioctyl azelate containing between 1% and 5% of viscosity of at least250 centistokes at 210 F.

11111111 00 HCHa 11011300 HHHH L 51 llll ll I III! l lll H I -o- I-0o--o-o--c :-r J0--c 2 0o-c-ol 1143- 0-11 HHH HH /.,HH .IHHHH wherein naverages about 34.

7. Tricresyl phosphate containing an amount sutficient to increase itsviscosity index of wherein n averages about 34.

8. A new composition of matter having the property of References Citedin the file of this patent improving the viscosity indices of diesterand phosphate U TED STATES PATENTS ester lubricants, and consisting of aconcentrate that con 2,465,150 Dickson 22, 1949 sists essentially of upto 95% of a vehicle freely miscible 5 fiuchs g 'f in said lubricant andof more than 5% of a polymer of a 2:485:376 g 1949 polypropylene glycolester of an unsubstituted low molecu- 2,562,878 Bl i A 7, 1951 larweight dibasic organic acid having a glycol-to-acid ,6 8,97 SandersonFeb. 17, 1953 mol ratio in the range of about 0.875 to 1.111, saidglycol 2,647,885 Biuica 4, 1953 containing a least oxypmpylene {witsSaid Polymer 5:233:32 1 3412 322555;1:211:11: $512. it; 132% having aviscosity of at least 250 centistokes at 210 F. 337 55 Mamszak et a1June 3, 1958 9. A method of preparing a polymer of a polypropylene2,929,786 Young et a1 Mar. 22, 1960 glycol ester of an unsubstituted lowmolecular weight di- OTHER REFERENCES basic acid, comprising: refluxinga polypropylene glycol Experiments in Organic Chemistry, by Fieser, 2nd

having at least seven oxypropylene units until the water Edition, 1941,D. C. Heath & 00., p. 398.

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF A LUBRICANTSELECTED FROM THE GROUP CONSISTING OF DIESTER LUBRICATING OILS ANDPHOSPHATE ESTER LUBRICATING OILS, AND A SUFFICIENT AMOUNT TO INCREASEAPPRECIABLY THE VISCOSITY INDEX OF SAID LUBRICANT OF A POLYMERIZEDPOLYPROPYLENE GLYCOL ESTER OF AN UNSUBSTITUTED, LOW MOLECULAR WEIGHTDIBASIC ORGANIC ACID HAVING A GLYCOL-TO-ACID MOL RATIO IN THE RANGE OFABOUT 0.875 TO 1.111 AND HAVING A VISCOSITY OF AT LEAST 250 CENTISTOKESAT 210*F. AND WITH AT LEAST SEVEN OXYPROPYLENE UNITS IN THEPOLYPROPYLENE GLYCOL RADICAL.